Another Parnall Elf

[Greyhead]

Thanks for that Dave, If anyone else has anything to add (or ask) just post away!


It's also a good idea to seal the printout before you cut it out to prevent smudges, I used clear spray lacquer from an automotive suppler.


The windscreens are simple affairs cut from acetate sheet. The fairing is from litho formed on this jig and the “bolts” are cut down pins. To make the job of painting the fuselage easier they were not fitted until it was ready for the final coat hence the painting of the fairing.





When forming shapes such as this from litho it is important to cut it oversize to allow for the stretching etc. However too much excess and it tends to stop the litho holding its shape and forms folds, so as you work keep trimming the edges, it soon becomes obvious where you’ve left too much material.


Don’t try to do the job in one go, form it partly to shape, trim off excess, form some more, trim again and so on. It’s amazing how complex a shape you can get out of a flat sheet of litho.

[Greyhead]

Just the undercarriage left to do and the fuselage is virtually finished. This was simple as the plan was near enough for me, except for the missing rear strut but this is non-functional and made from plastic tube. The piano wire was bent to shape and silver soldered, soft solder really isn’t up to the job even if the joins are bound with wire before soldering. The fairings are made from balsa but as it is impossible to get a sharp edge they are covered with litho.

The wheels are attached as per wonwinglo’s instructions in the tutorial forum except that I used a 14BA bolt instead of a split pin.

Sorry but no photos of the undercarriage being built, if anybody’s interested I can take some of it completed and fitted.

Now just stick on as many of the numerous brackets and strengthening plates as you can be bothered with, tape the joints and it’s ready for painting.

Remember to build light, having due regard for strength, because all these little bits and pieces soon start to pile on the weight. By the way I never bother to weigh my finished models, if it’s light it’ll fly that much better but if it’s over-weight it’s too late to do anything about it!

[wonwinglo]

Good tips on the decal printout Grahame,for anyone trying out this system buy a spray can of acrylic clear from the art shop,they have a soft sprayhead and this seals the otherwise water soluble ink used in these ink jets printers,just make sure that ink is really dry before even attempting to spray it on as a sealer.

Excellent litho tips as well,amazing material and it is free if you can find a friendly printer,we will be dealing more with this product in the near future here and explaining its many uses on models.

Great material,just keep it rolling ! good job that you had the foresight to photograph it all whilst building.

[Guest]

Grahame,

Have read the whole thread....Fantastic...!!!!!! Excellent workmanship and a Superb model that shows it too...!!! You are clearly an experienced modeller and the photos are a real credit to you. Keep up the good work. Posts like this are always a pleasure to read.

Regards.......Mark

[wonwinglo]

Just the undercarriage left to do and the fuselage is virtually finished. This was simple as the plan was near enough for me, except for the missing rear strut but this is non-functional and made from plastic tube. The piano wire was bent to shape and silver soldered, soft solder really isn’t up to the job even if the joins are bound with wire before soldering. The fairings are made from balsa but as it is impossible to get a sharp edge they are covered with litho.The wheels are attached as per wonwinglo’s instructions in the tutorial forum except that I used a 14BA bolt instead of a split pin.

Sorry but no photos of the undercarriage being built, if anybody’s interested I can take some of it completed and fitted.

Now just stick on as many of the numerous brackets and strengthening plates as you can be bothered with, tape the joints and it’s ready for painting.

Remember to build light, having due regard for strength, because all these little bits and pieces soon start to pile on the weight. By the way I never bother to weigh my finished models, if it’s light it’ll fly that much better but if it’s over-weight it’s too late to do anything about it!

*** Was just going to ask you about the weight Grahame ! you will need to give us some tips on the silver soldering ie materials to use,any special fluxes etc I like the way that you have done the lower curved axle bit on the undercarriage.

Biplanes do certainly add up on weight,all those metal fittings and wire etc the glide angle on my model is not too good she needs to be powered onto the ground and flared very precisely,I have never looped mine just content to observe that lovely biplane shape in the air.

[Greyhead]

*** Was just going to ask you about the weight Grahame ! you will need to give us some tips on the silver soldering ie materials to use,any special fluxes etc I like the way that you have done the lower curved axle bit on the undercarriage..

See "Silver Solder" in the Tutorials

[Greyhead]

That’s the fuselage finished ready for painting but if there’s anything you’re interested in that I’ve missed just let me know.


Now the wings. When building scale fabric covered wings we can’t use the normal modelling technique of top and bottom spars with or without sheeted leading edge (unless that’s scale of course!) as the fabric needs to sag in-between the ribs. Unfortunately this “D box” is what gives the wing most of it’s strength but I’ve devised a system which goes a long way to replacing the strength whilst retaining the scale appearance.


The wing has a front laminated spar and a spruce rear spar to which the hinge is attached, if the wings weren’t folding the rear spar could be missed out altogether or at least made from balsa to save weight.





The front spar is a spruce / balsa / spruce laminate with the balsa extended to go through the leading edge with the direction of the grain from LE to spar. The ribs are made in 2 pieces; the top front section is added after the composite spar with additional sections as “riblets”. The leading edge is 2 lengths of square balsa glued top and bottom of the balsa lamination.


Before covering, the ribs and more so the “riblets” are very vulnerable to damage whilst you do the other 101 necessary things to the wing. The answer here is to make a small hole in each of the pieces, it’s easier to do this before gluing in place, and then thread some strong cotton through the holes to make a “necklace”. After gluing in place, soak the cotton (button thread is the best) with thin cyano. It’s amazing how much this cotton also increases the torsional strength of the wing.

[Greyhead]

The rest of the main construction of the bottom wings was fairly straightforward. The hinges are pinned, again using model railway track pins, to the rear spar, glued with epoxy (see early photo) and finally given a few wraps with carbon fibre tows. The rear section of the bottom wings is hinged using commercial flat plate hinges and is held in place by 2 small magnets, the theory being that the air flow will keep them in position once the airspeed has built up and this has proved to be the case.


The photo below shows the mechanism for locking the wings in place. There is very little tension in the springs when locked, they’re just there to stop any movement caused by vibration. They lock into slots cut into free-floating tongues that pass right through the top centre section and fuselage.


The tongues were originally made from 1.5mm paxolin circuit board but having given it some thought I came to the conclusion that the model would have better flight characteristics if the wings stayed in the non-folded position during flight, so I replaced the tongues with ones made from carbon fibre sheet!





If you haven’t used carbon fibre tows before I can highly recommend them where some extra strength is needed without adding too much weight. Just a few strands glued using epoxy, the best but a bit messy, or cyano, watch out for the fumes, will greatly increase the strength. I also moulded the tailskid from carbon fibre tows and epoxy; it has produced a very strong, light and flexible job.

[Guest]

:great: oster_ke

[Greyhead]

An “eagle eye” has noticed that in the above posts I’ve said to thread the rib fronts to make a “necklace” before gluing in place but in the photo of the wing lock there’s no button thread to be seen! This is precisely why I’ve also said it is easier to do it that way. I built the bottom wings and then found out the hard way just how vulnerable the ribs were, i.e. I damaged a lot of them, that is when I worked out the idea of the thread and when it worked I incorporated it into the build for the top wings which was a lot easier.

[wonwinglo]

Great tips again,where do you get this carbon fibre tow material from Grahame ? locking those vulnerable ribs together with cotton thread like that makes good sense as well,it is flustrating to kick a few ribs whilst carrying out other tasks.

[Guest]

Try the "hi-tech materials" section of Freeflight Supplies in Norwich. The cap strips, ready made in a variety of thicknesses and widths are very useful for other uses. Longer lengths of ready made come in largeish loops. Used for edging Depron wings etc. There are a couple of suppliers on Ebay at the moment selling both tows and pultruded shapes. I`ll PM you later when I find them. Ironic that the oldest form of aeromodelling should be up there with the gas turbine boys in the use of modern materials. I`m sure somebody said that about balsa when it first appeared.

[Greyhead]

Barry

Our local model shop sells the carbon fibre tows; it comes wrapped around a piece of cardboard. It’s just lots of very thin strands of carbon fibre and am sure you should wear a respirator when cutting or sanding it!!

Grahame

[Greyhead]

At first sight the top wings appeared to be a fairly straightforward build; external pushrod from fuselage to wing then torque rod to the aileron. As is often the case, first impressions can be deceiving; the pushrod connection has to accommodate the folding of the wing and the torque rod isn’t inline with the aileron hinges.


The top wings were constructed using the same method as described early except that the rear spar is also a spruce / balsa / spruce laminate. In future I’ll laminate all spars as there is quite a weight saving and surprisingly the result appears to be stronger.


The torque rod is made in 2 pieces, the ends are made first then the rod fed through from both ends and joined with a short length of tube, when everything is lined up and slop free the joint is soldered.


First a general view.





I couldn’t figure out how the full size linkage worked so I decided to use a crank and slot, the photos are self-explanatory.





In this view you can also see one of the ply hinges, for strength they have a hole cut and are threaded onto the spar








At this point I’ll have to “do the time warp” and jump forward several months. Although all seemed satisfactory at this time, when I fitted the radio the ailerons wouldn’t neutralise. To this day I don’t know what was wrong or why what I did corrected it, but I made a new slot near the TE of the aileron, turned the crank through 180º and hey presto no more problem. Incidentally, the fact that the torque rod was joined made this modification easy. As you can see this is not quite as good from a scale point of view as the crank is now visible but only when the ailerons are raised or lowered.

[Guest]

It is good the that some modellers are not blinkered in the way that they build their models, the use of thread to strengthen the fragile sub ribs is pure genius, (who would of used thread). I am really enjoying reading this thread (excuse the pun) and look forward with anticipation for the next episode.

A big well done